Method for simultaneous non-contact electrochemical plating and planarizing of semiconductor wafers using a bipiolar electrode assembly

ABSTRACT

Simultaneous non-contact plating and planarizing of copper interconnections in semiconductor wafer manufacturing is performed by providing relative motion between a bipolar electrode and a metallized surface of a semiconductor wafer without necessary physical contact with the wafer or direct electrical connection thereto.

BACKGROUND OF THE INVENTION

The present invention relates to the simultaneous electrochemical metalplating and planarization of integrated circuit wafers to formmultilevel integrated circuit structures.

Today's semiconductor industry is beginning to adopt a manufacturingprocess called "damascene" for forming interconnect lines and vias formulti-layer metal structures that provide the "wiring" of an integratedcircuit. The damascene technique involves etching a trench in a planardielectric (insulator) layer and filling the trench with a metal such asaluminum, copper, or tungsten. A technique called "dual-damascene" addsetched vias for providing contact to the lower level as the damascenestructure is filled. There are several different ways to manufacture thedamascene structure in the dielectric layer as practiced in the art anddescribed in "Making the Move to Dual Damascene Processing",Semiconductor International, August, 1997 hereby incorporated byreference. When copper is used as the filling, typically a layer ofanother material is first deposited to line the trenches and vias toprevent the migration of the copper into the dielectric layer. Thismigration barrier can be deposited by chemical vapor deposition (CVD),physical vapor deposition (PVD), or electroless deposition. In additionto the migration barrier, sometimes a seed layer of the plating metaland/or other metals are applied to serve as a good site for electrolessor electrolytic plating.

The filling process can be accomplished by plasma deposition,sputtering, or electroless or electrolytic deposition onto a seed layer.To achieve good fill of the typical micron to sub-micron wide trenchesand vias, extra metal is deposited in the process, such metal coveringareas of the wafer above and outside the trenches and vias. Afterfilling, the extra metal must be removed down to the dielectric surfacewhile leaving the trenches and vias filled in a process called"planarization". Standard chemical mechanical planarization (CMP) can beused to provide a planarized surface and metal removal.

As an alternative to CMP, electrochemical etching (ECE), electrochemicalpolishing (ECP), electropolishing or electrochemical planarization (ECP)has been used. For the purpose of this application, the terms"electrochemical polishing", electropolishing, "planarizing" and"electrochemical planarization" will be used interchangeably as they arein literature. The end goal is to have a very flat and smooth surface,the small differences between the terms is that the polishing desires tohave a very smooth surface, while planarization desires to flatten-outtopology and produce a flat smooth surface. "Electrochemical etch"however has a different purpose, that is to remove material, generallyuniformly, without regard to surface flatness.

U.S. Pat. No. 5,096,550 Mayer et al., entitled "Method And Apparatus ForSpatially Uniform Electropolishing And Electrolytic Etching" describesconventional electropolishing with the addition of a non-conductingchamber or cup with a hole between the anode and the cathode, theworkpiece electrically attached to the anode and the cathode external tothe cup and above the layer of the hole. This approach is said tominimize the flow of hydrogen bubbles to the anode workpiece surface.For semiconductor wafers, which are bulk non-conductors, it is necessaryto attach the electrode (anode) directly to the metallized front surfaceof the wafer, thereby limiting wafer surface area that can be used foractive devices.

U.S. Pat. No. 5,256,565 Bernhardt et al., entitled "ElectrochemicalPlanarization" describes a multi-step process, teaches separateapparatus for each step, first forming trenches or vias in a dielectriclayer on a semiconductor substrate, optionally followed by one or moremetal seed layers, not disclosed as how to form them, followed by metaldeposition using conventional electroplating or electroless plating,followed by electrochemical polishing to form substantially flatdamascene structures, optionally stopping before the metallized surfacebecomes partially eroded away and following with ion beam milling toremove the rest of the top surface of the metal, leaving the metal inthe trenches and vias.

U.S. Pat. No. 5,567,300 Datta et al., entitled "Electrochemical MetalRemoval Technique For Planarization Of Surfaces" describes anelectrochemical cell and a planarization method for planarization ofmultilayer copper interconnections in thin film modules. Theelectrochemical cell and method is described as providing planarizationof the first electrode surface (the wafer) using a scanning parallelsecond electrode with an electrolytic solution combined with a resistivesalt mixture, ejected through the scanning electrode surface throughbuilt in nozzles, along with the appropriate voltage supply. Again, forsemiconductor wafers, which are bulk non-conductors, it is necessary toattach the electrode (anode) directly to the metallized front surface ofthe wafer, thereby limiting wafer surface area that can be used foractive devices.

U.S. Pat. No. 5,344,539 Shinogi et al., entitled "Electrochemical FineProcessing Apparatus" describes an apparatus for electrochemicallyperforming an adding processing and removing processing of a substancesuch as a metal or polymer in a solution in order to produce a structurehaving a high aspect ratio. The apparatus comprises a container for theelectrolytic solution, a first potential between the adding electrodeand the support to be plated, a second potential between a removingelectrode and the support to be plated, the second potential beingopposite to the first potential, and a potential means. Shinogi et al.teaches applying the two separate but opposite potentials at the sametime, or by first applying the adding potential between the addingelectrode and the support to be plated and then switching to theremoving potential between the adding electrode and the support to beplated. Shinogi et al. is limiting in that there is a requirement fortwo concurrent potentials of opposite polarity, or a stepwise processwhereby the addition potential is followed by the removal potential.Shinogi et al. is advantageous over the previously described U.S. Pat.Nos. 5,096,550, 5,256,565, and 5,567,300 previously described in thatsimultaneous addition and removal of material is possible with twoseparate applied potentials. However, if the Shinogi et al. apparatuswere used for semiconductor wafers, which are bulk non-conductors, itwould be necessary to attach a common electrode directly to themetallized front surface of the wafer, thereby limiting wafer surfacearea that can be used for active devices.

U.S. Pat. No. 5,531,874 Brophy et al., entitled "Electroetching ToolUsing Localized Application Of Channelized Flow Of Electrolyte", U.S.Pat. No. 5,536,388 to Dinan et al., entitled "Vertical Electroetch ToolNozzle And Method", U.S. Pat. No. 5,543,032 to Datta et al., entitled"Electroetching Method And Apparatus" and U.S. Pat. No. 5,486,282 Dattaet al., entitled "Electroetching Process For Seed Layer Removal InElectrochemical Fabrication Of Wafers" all use a linear scanning methodof localizing the electrochemical reaction and are optimized in slightlydifferent ways from etching both sides of a workpiece, to verticalscanning, to a salt solution combined with an electrolyte, to a processfor forming C₄ bumps on a substrate, respectively. All of these methodsrequire an electrode attachment to the metallized seed layer ormetallized surface when the workpiece is a semiconductor wafer therebylimiting wafer surface area that can be used for active devices.

U.S. Pat. No. 5,695,810 Dubin et al., entitled "Use Of Cobalt TungstenPhosphide As A Barrier Material For Copper Metallization" describes atechnique for electrolessly depositing a Co WP barrier material ontocopper and electrolessly depositing copper onto a Co WP barrier materialto prevent copper diffusion when forming layers and/or structures on asemiconductor wafer. This patent teaches the formation of a damascenestructure on a semiconductor wafer by a combination of electrolessdeposition and chemical mechanical polishing. Also the patent teachesthe formulation of a via structure also using electroless deposition.This patent also discloses separate co-pending patent applicationsentitled "Electroless Cu Deposition On A Barrier Layer By Cu ContactDisplacement For ULSI Applications," Ser. No. 08/587,262, filed Jan. 16,1996, now U.S. Pat. No. 5,891,573; "Selective Electroless CopperDeposited Interconnect Plugs For ULSI Applications", Ser. No.08/582,263, filed Jan. 16, 1996, now U.S. Pat. No. 5,674,787; and"Protected Encapsulation Of Catalytic Layer For Electroless CopperInterconnect", Ser. No. 08/587,264, filed Jan. 16, 1996, now U.S. Pat.No. 5,824,599. Electroless deposition as taught by Dubin et al. has someadvantages in forming a damascene structure onto semiconductor wafers,but it may also have disadvantages, such as the quality of the adhesionof the barrier layer to the material being plated and possibleundesirable contamination of the semiconductor due to the metal catalystused to initiate the deposition of the barrier metal. The biggestconcern in the Dubin et al. process is the inherent difficulty incontrolling any electroless deposition process uniformity as compared toan electroplating process, especially for the fine features present insemiconductor manufacturing.

One of the drawbacks to the established methods of producing a damascenestructure is that it requires separate steps of filling and thenplanarizing the metal surface. In between the filling and planarizing,sometimes a moderate temperature anneal is performed on the depositedmetal to decrease resistivity and to form a more stress free deposition.If the filling and planarization of the damascene structure could beaccomplished in a single process in place of the fill then planarizesteps, substantial cost savings would result. Additionally, the multiplecleaning steps after filling, annealing and planarizing could bereplaced with a cleaning and annealing after the damascene process.

What is needed is a method and apparatus for simultaneous non-contactelectrochemical metal plating and planarization of semiconductor wafersthat does not require a physical electrical connection to the surface ofthe semiconductor wafer.

BRIEF SUMMARY OF THE INVENTION

The present invention permits the simultaneous non-contact plating ofmetal and planarization of metal for interconnections on semiconductorwafers by providing relative motion between a bipolar electrode and ametallized surface of a semiconductor wafer, the bipolar electrodeholding both the anode and cathode and eliminating the need for directelectrical connection to the wafer.

Specifically, the present invention provides a non-contact method ofconcurrent metal plating and planarization of a semiconductor waferhaving a metallized surface by performing the steps of positioning abipolar electrode assembly opposite the metallized surface of thesemiconductor wafer, the bipolar electrode assembly having an anode andcathode adjacent to the metallized surface of the wafer and separatedalong an axis parallel to the metallized surface while bathing a regionbetween the anode and cathode and metallized surface of thesemiconductor wafer in an electroplating solution. Relative motion isprovided between the electrode assembly and the metallized surface ofthe semiconductor wafer along the axis with the anode preceding thecathode while a voltage is applied across the anode and cathode so as toplate with metal the metallized surface of the semiconductor wafer inthe region of the anode and to concurrently planarize the semiconductorwafer in the region of the cathode through action of current flowbetween the anode and cathode.

It is thus one object of the invention to provide an apparatus andmethod that electrochemically plates and planarizes a metalized surfaceon a wafer in one step to form a multilevel integrated circuit structurewithout having to rely on mechanical electrical contacts to the wafermetallized surface. By eliminating the need to attach an electrode tothe metallized wafer surface, the control of the process is greatlyenhanced over standard electroless plating and planarizing techniquesand electrode attachment defects are not incurred.

It is another object of the invention to provide a system employing abipolar electrode assembly. By moving the electrode assembly over themetallized wafer surface, the instantaneous electrochemical process isconfined to a small area on the wafer surface providing more uniformsolution resistance, more uniform deposits, better plating andplanarization, better localization of current, and better temperaturecontrol.

The electroplating solution may be recirculated through a heat exchangerand across the wafer near the anode and cathode.

It is thus another object of the invention to assure that each part ofthe wafer surface and each wafer sees a relatively constant set ofthermal and chemical conditions.

A first and second electroplating solution delivery channels may be usedto provide electroplating solution separately to the anode and cathode.Further, an electroplating solution removal channel may be positionedbetween the first and second electrodes for withdrawing electroplatingsolution from the wafer.

Thus it is another object of the invention to permit the optimization ofthe electroplating solution to the distinct environments of the anodeand cathode.

The foregoing and other objects and advantages of the invention willappear from the following description. In this description, referencesare made to the accompanying drawings which form a part hereof, and inwhich there are shown by way of illustration, the preferred embodimentof the invention. Such embodiment does not necessarily represent thefull scope of the invention, however, and reference must be madetherefore to the claims for interpreting the scope of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1(a) is a fragmentary elevational, cross-sectional view of asemiconductor wafer showing the active device layer and first innerdielectric layer that has been planarized and subsequently patterned,etched and via holes filled;

FIG. 1(b) is a figure similar to that of FIG. 1(a) also showing adielectric layer and a layer of photoresist;

FIG. 1(c) is a figure similar to that of FIG. 1(b) after patterning,etching trenches, and removing the photoresist;

FIG. 1(d) is a figure similar to that of FIG. 1(c) after a barrier metaland seed layer have been deposited;

FIG. 1(e) is a figure similar to that of FIG. 1(d) after a metal filmhas been deposited;

FIG. 1(f) is a figure similar to that of FIG. 1(e) after the metal layerhas been planarized;

FIG. 2 is a schematic cross sectional view in elevation of a prior artelectroplating cell, showing anode and cathode (plating occurs onto thecathode);

FIG. 3 is a schematic cross sectional view in elevation of a prior artbipolar electrode electroplanarization cell, showing anode, cathode, andworkpiece to planarize;

FIG. 4 is a schematic cross sectional view in elevation of a bipolarelectrode electroplating cell of the present invention providing platingand planarizing on a single conducting side of the workpiece;

FIG. 5 is a figure similar to FIG. 4 showing the bipolar electrode ofthe present invention operating to plate then planarize a wafer havingtrenches, the bipolar electrodes exaggerated for clarity;

FIG. 6 is a perspective view of the bipolar electrode of the presentinvention showing a scanning assembly, the electroplating solutioncontainer and various power and fluid lines;

FIG. 7 is a elevational, cross-sectional view of the electrode assembly,showing the anode and cathode, fluid lines, and insulators; and

FIG. 8 is block diagram view of the main parts of the apparatus of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION The Damascene Process

FIG. 1, (a through f) shows a set of cross-sections illustrating oneprior art method of manufacturing a damascene structure. Kaana et al."Dual Damascene: A ULSI Wiring Technology", Ryan et al. "The EvolutionOf Interconnection Technology At IBM", Peter Singer, Editor "AMDDevelops Electroplated Copper Damascene Process", "Electroless CuDeposition Simulated", and "Making the Move to Dual DamasceneProcessing" provide further details on the damascene process and arehereby incorporated by reference.

FIG. 1(a) shows active device layer 10, with an inner layer dielectric(ILD) 20, and tungsten plugs (filled vias) 30.

The damascene process then begins with a deposition of dielectricmaterial 40 as shown in FIG. 1(b), and photoresist 50. The photoresistis patterned, developed, and etched, followed by etching of thedielectric layer to form the damascene trench 60 shown in FIG. 1(c).

A barrier and adhesion layer 70 is deposited by CVD, PVD, or electrolessplating, followed by the deposition of a thin seed layer 80 by similarmethods as shown in FIG. 1(d). The seed layer 80 may be capped by asacrificial metal film to provide further protection until the nextprocess step is taken as described in DeSilva & Shacham-Diamand, "ANovel Seed Layer Scheme to Protect Catalytic Surface for ElectrolessDeposition".

FIG. 1(e) shows a metal fill 90 of the trench. The metal could have beenfilled from CVD, PVD, electroless or electrolytic plating. To planarizethe metal fill 90 several methods can be used; CMP, laser leveling,etching, or electrochemical planarization (electropolishing).

FIG. 1(f) shows the planarized surface 100.

It is important to understand that each of the methods of depositingmetal into the trenches and vias and each of the methods of planarizingthe metal to form the damascene process has its own set of features andcharacteristics well known in the art. For example, one method may fillnarrow trenches better, another method may work better filling trenchesif the trench walls are slightly angled wider at the top. Prior artmethods of planarization of the metal surface also varies depending onthe method used. Pure chemical etching of the metal produces inferiorresults since it tends to attack all exposed surfaces and would etchaway at the depression that tends to form as a result of the fillingprocess, as fast as the more planar metal surface. The etch wouldgenerally result in a dishing of the metal conductor.

CMP tends to work very well for planarization if the correct slurry andprocess parameters are used. The higher the surface feature, the fasterthe CMP process removes it. Electrochemical planarization is attractivesince it does not require a slurry to operate and does not scratch thesurface as CMP may. One skilled in the art of CMP and electrochemistrycan select and choose the most appropriate method of filling andplanarizing the metal surface. More details on Electrochemicalplanarization are given in Bernhardt et al., "ElectrochemicalPlanarization for Multi-Level Metallization of Microcircuitry" andContolini et al., "Electrochemical Planarization for Multi-LevelMetallization".

Prior Art Electroplating and Planarization

FIG. 2 shows prior art in standard electroplating or planarization. Aconducting anode 200 of the metal to plate is connected to an electricalconductor 150 by attachment 160. The electrical conductor 150 is alsoconnected to the positive terminal of a voltage source 220. The metalobject to plate, a workpiece 210 is connected to an electrical conductor110 at attachment 120. The electrical conductor 110 is also connected tothe negative terminal of the voltage source 220 forming a cathode in anelectrochemical cell. The anode and cathode are suspended within a tank(not shown) containing the electroplating (working) solution with themetal ions that will plate out onto the workpiece 210, since it is acathode in the cell. One skilled in electroplating realizes that most ofthe plating of metals will take place on the workpiece surface 130facing the anode. Also, most of the metal that is de-plated from theanode 200 comes from the anode surface 170 facing the workpiece 210.This behavior is governed by the electric field, represented by arrow151 , caused by applying a voltage across the electrochemical cell byvoltage source 220. Since the anode 200 and the cathode 210 aresuspended in a conducting or electrolytic solution, electrical currentwill flow from the anode 200 to the cathode 210 in the same direction asthe electric field.

As shown in FIG. 3, if one were to add an additional electrode for thecathode 180 and instead of attachment 120 in FIG. 2, connect electricalconductor 110 to the new cathode 180 at connection 221, a bipolarelectroplating cell would be formed. The electric field from the anode200 to the cathode 180 is represented by arrow 151 shown in FIG. 3.Since the anode 200, workpiece 210, and the cathode 180 are allconducting and immersed within an electrolytic solution duringoperation, current flows from the anode 200 through the electrolyte (notshown) to the surface 130 of the workpiece 210 and through the workpiece210 to workpiece surface 140, and through the electrolytic solution (notshown) to the cathode 180 by action of the applied voltage source 220.In effect, the workpiece becomes bipolar in that one surface 130 isnegatively charged with respect to the anode 200 while the other surface140 is positively charged with respect to the cathode 180. Due to thefact that the surface 130 of the workpiece 210 is negative with respectto the anode 200, electroplating of metal occurs on surface 130.However, due to surface 140 being positive with respect to cathode 180,de-plating of metal may occur at surface 140. This bipolar effect allowselectroplating of conducting objects without having to have a separateconductor attached to the workpiece. If only surface 130 of theworkpiece 210 is conducting with surface 140 being essentiallynon-conducting, plating of metal on surface 130 will still take placebut will be highly non-uniform, since the current flow through the celland workpiece must flow around the non-conducting surface 140 and intothe edge of the conducting surface 130. Semiconductor wafers with ametal seed layer are typically only conducting on the seed layer sideand not the back side of the wafer. Therefore, contactlesselectroplating of the metal seed layer of semiconductor wafer workpiecein a bipolar cell will not work very well. Currently, electroplatedmetal seed layers on a semiconductor wafer workpiece require electrodeattachments to the seed layer and are electroplated as shown in FIG. 2.Electroless plating of the metal seed layer does not require electrodeattachments however.

For electropolishing or electroplanarization, the potentials shown inFIG. 2 and FIG. 3 are reversed and many times a different electroplatingsolution is used.

For prior art electroplanarization of a semiconductor metal surface,electrode contacts are required on the metal surface. Conventionalbipolar planarization will not work satisfactorily with semiconductormetal surfaces due to the same reasons that bipolar electroplating doesnot work well, the semiconductor is only metallized on the frontsurface, while its back surface is a non-conductor (typically an oxidefilm). The counterpart to electroless plating is chemical etching.Chemical etching of the metallized surface will not produce satisfactoryplanarization of the surface.

Thus, if the desired process to planarize is electropolish, electrodeattachments must be made to the metal layer. These attachments show upin the final planarized surface as defects. CMP does not have thesedefects.

If the manufacture of the damascene structure by simultaneouselectroplating and electropolishing did not require electrode contactsto the wafer surface, a finer and higher quality product would result.Additionally, if the requirement for two separate potentials aspracticed in U.S. Pat. No. 5,344,539, Shinogi et al., were reduced to asingle potential, a simpler and more reliable system would result. Thepresent invention accomplishes all of these goals.

Single Sided Bipolar Electroplating and Planarization

Referring to FIG. 4, a single sided bipolar electrode 431 of the presentinvention provides for simultaneous plating and deplating on a singleconducting side of a wafer 430. The bipolar electrode 431 includes ananode 200 and cathode 180 arranged to be positioned on the samemetallized side 250 of the workpiece, plus add an insulator block 230placed between them. When positioned for use, the anode 200 and cathode180 extend substantially perpendicularly from the metallized face of thewafer 430 and are spaced apart along a scanning direction 300 to bedescribed but which is generally parallel to the metallized face of thewafer 430. The anode 200, the cathode 180 and the insulator block mayhave a length measured along the metallized surface of the wafer 430perpendicular to the scanning direction 300 so as to span the widestpart of the wafer 430 so that a portion of the anode 200 and the cathode180 may be adjacent to the entire area of the metallized surface of thewafer along that span. The anode 200 and cathode 180 are positioned toclosely approach the surface of the metallized surface of the wafer 430but not to contact that surface directly.

In FIG. 4, applying a positive potential from voltage source 220 throughelectrical conductor 150 and connecting to anode 200 at attachment 160,while applying a negative potential through electrical conductor 110 andconnection 221 to cathode 180, would result in electroplating occurringto the area 252 immediately under the anode 200 and deplating orelectropolishing occurring to the area 254 immediately under the cathode180 due to the standard bipolar electrochemical effect. Thissingle-sided approach is utilized in the present invention.

FIG. 5 is an elevational, cross-sectional view to illustrate thesimultaneous electroplating and planarization of the wafer. The distancebetween anode and cathode has been reduced for illustration purposes.The anode 510, cathode 570, and cathode insulated separator block 550are caused to move relative to the metallized wafer 430 by scanningmeans such as a motor driven lead screw or the like in the scanningdirection 300. Electroplating solution 161 flows between the anode 510and a part of the wafer surface in the direction indicated by the arrow.Electrolytic solution 222 flows between the cathode 570 and a differentpart of the wafer surface in the direction indicated by the arrowhead.The anode 510 and cathode 570 operate on the same side of the wafer, notopposite sides as in conventional bipolar plating. Individually, theanode and cathode may be of different size, shape, distance from thesurface of the wafer or area to enhance or reduce the current densitiesunder the electrodes and thereby the plating rates, respectively. Thepower lines 480 and 485 are connected to the anode and cathode,respectively, and provide the operating voltage and current from powerunit 660. Metal 340 is electroplated onto the wafer 430 as the anode 510moves over the metallized side 250 of the wafer 430 in the scanningdirection 300 and is removed from the surface as the cathode 570 passesover the surface.

A trench 111 is shown partially plated as the anode approaches itslocation. The thickness 310 of metal that needs to be added in platingis approximately three (3) times as thick as the widest trench 320 iswide to ensure that the trenches are completely filled beforeplanarization. The electroplating solution 161 is withdrawn from thewafer surface as is illustrated by the arrow. The anode/cathodeinsulated separator block 550 forces the current to flow into themetallized wafer surface and not just between the anode and cathode.Metal 330 is electropolished as the cathode moves over the wafer. Atrench 181 is shown fully planarized after the cathode has passed itslocation. In this process, the thickness of metal 310 that was added bythe anode 510 is substantially removed from the planarized surface asthe cathode 570 passes over.

The spent electrolytic solution 222 is withdrawn from the wafer surfaceas is illustrated by the arrow. The quantity of plated material removedby the cathode depends on the exact compositions on the layer, the fillmetal, the chemistry, the applied potential, the current, and whether ornot a surface passification chemical has been added to protect thefilled trenches as will be understood from this description to one ofordinary skill in the art. The preferred process uniformly plates metal,planarized it, and then rinses and applies a passification rinsechemical that substantially passifies the surface of the filledtrenches. When the electrodeposited metal fill is copper, a dilute 0.005Molar solution of benzotriazole (BTA) combined with rinse deionizedwater to form the protective layer is used.

The remaining exposed barrier layer 70 (shown in FIG. 1) may be removedby standard etching processes, such as wet etch, vapor etch, spray etch,plasma, or even CMP, since the surface of the wafer had just previouslybeen substantially planarized with the present invention. Selection ofthe etch method and chemistry depends on the barrier metal chemistry.Typically barrier metals may be tungsten (W), (Ti), titanium nitride(TiN), tantalum (Ta), tantalum nitride (TaN) or other alloys andrefractory nitrides.

The bipolar electrodes allow for the use of two separate electrolyticsolutions, one optimized for plating and used on the anode side of theelectrode assembly and one optimized for electropolishing the platedstructure on the cathode side. In the preferred embodiment, a singleelectroplating solution is used for both sides of the electrode assemblyfor electroplating and planarizing.

Adjustments to the process may be made by varying the individualdistances of the anode and cathode from the wafer surface, the distancesbetween the electrodes, the effective surface area of the electrodes,the shape of the electrodes, the applied potential, the scanning speed,scanning direction, and the current. The process may be optimized byvarying these parameters as a function of the selected chemistries.

Referring to FIG. 6, a perspective view of the electrochemical cell 400shows a wafer 430 to be processed by being loaded, process side up, intoa wafer holding assembly 435 thus allowing access to the metallizedlayer on the wafer surface. The inner portion of the wafer holdingassembly 435 is recessed to allow the wafer surface to be substantiallyflat with the surface of the remaining part of the holder. The wafer isheld in place with a small vacuum chuck (not shown) or with gravityalone. The present implementation of the invention is a system toprocess 300 mm diameter or smaller semiconductor wafers. There is nopractical limiting feature that would prevent the design of a systemutilizing the present invention for use with 400 and 500 mm wafers orlarger, or with rectangular objects such as flat panel displays. Thescanning assembly 425 holding the electrode housing 440 is caused tomove over the wafer 430, in the scanning direction 300, by means of thedrive motor 470, and scanning table 460 mounted to the baseplate 410.Electroplating solution is fed to the scanning assembly 425 through thefluid input line 490. Spent electroplating solution for plating iswithdrawn from the scanning assembly 425 through the fluid withdrawalline 495. The power lines 480 and 485 provide voltage to the scanningassembly 425. The liquid containment 420 prevents unwanted fluidcontamination and allows draining of rinse waters, electroplatingsolution, or surface passivation fluid as needed through fluid line 450.Typically, the wafer is processed in one or more scans of the scanningassembly 425.

FIG. 7 is an elevational, cross-sectional view of the bipolar electrodeassembly 500, within the electrode housing 440, showing the anode 510and cathode 570. This linear bipolar anode cathode assembly is preciselyscanned over the wafer surface, while electroplating solutions areflowed to provide contact between the bipolar anode/cathode assembly andthe wafer surface. The anode 510 and cathode 570 operate on the sameside of the wafer, not opposite sides as in conventional bipolarplating. The anode and cathode are made preferentially of an inertelectrical conductor such as graphite, carbon, platinum, or other metalinert to the electrochemistry. The anode or cathode or both could bemade of the metal being plated onto the wafer surface if so desired.

The power lines 480 and 485 shown in FIG. 6 are connected to the anodeand cathode, respectively, and provide the operating voltage andcurrent.

Electroplating solution to the wafer surface is provided through theanode-side fluid input line 520, the distribution manifold 525, and thebrush 595. The brush is typically non-conducting, fibrous or open poreporous, and flexible. The brush 595 extends the length and width of thebipolar electrode assembly 500 and is thinner under the insulatingseparator block 550. It is preferred to have the electrodes slightlyrecessed with respect to the separator block 550 to enhance theshielding that the block 550 provides to the electric field between theanode and cathode. The anode and cathode may be of a different size,shape, or area to enhance or reduce the current densities under theelectrodes and thereby adjust the relative plating and planarizing rate.

The brush 595 can be operated in a similar manner as in conventionalbrush-plating or brush-electropolishing in that it can actually rub thesurface that is being planarized, or the brush may be operated slightlyoff of the wafer surface.

The spent electroplating solution for plating is withdrawn from thewafer surface through the brush 595, an anode-side withdrawal manifold545, and an anode-side fluid withdrawal line 540. The exterior anodeinsulator block 530 helps to mount the anode 510 and the various otherparts of the anode side of the assembly. The anode/cathode separatorblock 550 provides a mount for the anode and cathode and the fluid linesand forces the current to flow into the metallized wafer surface and notjust between the anode and cathode. Electrolytic solution forplanarization flows between the wafer surface and the cathode through acathode-side fluid input line 560, a distribution manifold 565, and thebrush 595. The spent electrolytic solution for planarization iswithdrawn from the wafer surface through the brush 595, through acathode-side withdrawal manifold 585, and through a cathode-side fluidwithdrawal line 580. The exterior cathode insulator block 590 helps tomount the cathode and the various other parts of the cathode side of theassembly. The anode/cathode fluid coupling line 555 is used when thesame chemical solution is used to both plate on the anode side andplanarize on the cathode side of the assembly.

Referring to FIGS. 6 and 7, the bipolar electrode assembly 500 allowsfor the use of two separate electroplating solutions, one optimized forplating used in the anode side of the assembly and one optimized forplanarization used on the cathode side. When two such electroplatingsolutions are used, the electroplating solution for plating flows intothe electrode housing 440 through fluid input line 490 and is withdrawnthrough fluid withdrawal line 495 shown in FIG. 6. Fluid input line 490connects to anode-side fluid input line 520 and fluid withdrawal line495 connects to the anode side fluid withdrawal line 540. Theelectroplating solution for planarization flows into the electrodehousing 440 through an additional fluid input line (not shown) and iswithdrawn through an additional fluid withdrawal line (also not shown).

Referring to FIG. 8, the main parts of the complete apparatus consistingof the fluid pumping assembly 600, the electrochemical cell 400 aspreviously described, the electrochemical power unit 660, the controlcomputer 610, and the scan motor controller 640 are shown. In the fluidpumping assembly 600, an electroplating solution is drawn from thefeed/return tank 710 through feed line 770 by delivery pump 740 which inturn feeds electroplating solution to the electrode housing 440 throughthe heat exchanger 720, filter 730, three way valve 735 and fluid inputline 490. Spent electroplating solution is withdrawn from the electrodehousing 440 through fluid withdrawal line 495 through three way valve685, by withdrawal pump 690, and delivered through line 780 to thefeed/return tank 710. Chemical-B input line 675 is used to initiallyintroduce electroplating solution into the system, top off the systemduring normal operations, or flush the system with de-ionized water.Chemical-A input line 755 is used to introduce an alternate chemicalinto the system for additional processing, such as adding a passivatorafter the plating and planarizing process, or in rinsing the wafer withdeionized water as is understood in the art. Typically, the alternatechemical is allowed to flow to drain. The process chemicals can be usedas a single pass system or can be recirculated with or withoutreplenishment or purification. The replenishment or purification processcan involve heating, cooling, filtration or chemical modification of theprocess chemicals as is understood in the art. The control computer 610communicates (commands and receives data) with the pump motor controller670, and valves 685 and 735 through control and power lines 760, 695 and745, respectively. The control computer 610 also communicates (commandsand receives data) with the electrochemical power unit 660 and the scanmotor controller 640 through control lines 650 and 630, respectively.The pump motor controller 670 controls pumps 690 and 740 through controland power lines 680 and 750, respectively.

If separate solutions are used for the anode and cathode a secondpumping assembly (not shown) is hooked up in a similar manner as thesingle unit shown in FIG. 8.

Additional chemical lines and chemicals may be added to the electrodeassembly to provide for a chemical treatment between plating andelectropolishing, before plating to condition the surface for plating,or after electropolishing to add a passivation layer. The additionalsteps may be added to the process through the use of multiple electrodeswithin the electrode assembly, with the anode and cathode alternating,so that the process may be accomplished in a single pass of theassembly. Separate assemblies, each with specific processes, may becaused to pass over the wafer to accomplish the same.

The electrode assembly has been described moving with the wafer fixed.The current invention allows the electrode assembly to be fixed with thewafer moving, or with both moving relative to each other.

In addition, while the orientation of the assembly is shown with theactive side of the workpiece upwards with respect to gravity, theinvention would work also in any orientation with respect to gravity.The invention has been described in terms of linear electrodes andrelative linear motion between the electrode assembly and workpiece, oneskilled in the art can realize that changing the shapes of theelectrodes and changing the type of relative motion may also bepracticed by this invention. Thus circular or orbital relative motions,combinations of relative motions, combination of relative motions andvarious electrode shapes may be practiced by this invention. Orbitalmotion, as used herein, refers to movement of an object in an orbitwithout angular rotation about a center. Circular motion, as usedherein, refers to angular rotation of an object about a center. Combinedmotions may be achieved by moving the wafer with one motion and theelectrodes with another motion or by moving either the wafer orelectrodes with multiple alternating or simultaneous motions. A typicalcombination motion might be a linear tangential sweeping of theelectrodes across the wafer as the wafer is moved with circular motionlike a record or CD. During retrograde motion between the electrode andthe wafer opposite the scanning direction, the voltage across the anodeand cathode may be switched off or reversed in polarity. The inventionhas also been described in terms of a single anode and cathode, however,the invention may be practiced with multiple alternating anode andcathode electrodes in a single electrode assembly, each of the same ordifferent area and/or shape or may be practiced with multiple electrodeassemblies, each configured to provide for desired results as oneskilled in the art may realize.

The preferred embodiment is practiced with a single electrolyticsolution used for both electroplating and electroplanarizing. Table 1lists the makeup of the preferred electrolytic solution.

                  TABLE 1                                                         ______________________________________                                                  Low       High      Preferred                                       ______________________________________                                        Copper Sulfamate                                                                        50     g/L    150  g/L  100  g/L                                      Ammonium 100 g/L 150 g/L 125 g/L                                              Sulfamate                                                                     Sulfamic Acid 20 g/L 30 g/L 25 g/L                                            Chloride ions 50 ppm 100 ppm 75 ppm                                           Dextrose 0 g/L 10 g/L 8 g/L                                                   Triethanolamine 0 g/L 6 g/L 3 g/L                                             pH 1  3.5  2 (adj with                                                              sulfamic acid)                                                          Current Density 2 A/m2 37 A/m2 10 A/m2                                      ______________________________________                                    

An alternative electroplating solution is listed in Table 2.

                  TABLE 2                                                         ______________________________________                                                  Low       High      Preferred                                       ______________________________________                                        Copper fluoborate                                                                       200    g/L    550  g/L  300  g/L                                      Fluoboric acid 5 g/L 60 g/L 25 g/L                                            pH 0.2  2  1 (adj with                                                              fluoboric acid)                                                         Current Density 5 A/m2 40 A/m2 15 A/m2                                      ______________________________________                                    

When processing wafers, the system is operated in a programmed currentmode, the current directly proportional to the area of the wafer underthe scanning assembly. The computer control system controls the currentto the scanning electrode as a function of the location of the scanningassembly on the wafer. Depending on the width of the widest trench to befilled, the effective electropolishing current density is between 2 to37 amps per square meter (ASM) preferably 10 ASM and the preferredscanning speed is between 4 and 8 inches per minute. One of ordinaryskilled in the art can readily further optimize the operation of thepresent invention by selecting alternate chemistries, and varying thecurrent, and scan speed.

As mentioned, the present implementation of the invention is a system toprocess 300 mm diameter or smaller semiconductor wafers. There is nopractical limiting feature that would prevent the design of a systemutilizing the present invention for use with 400 or 500 mm wafers orlarger, or with rectangular objects such as flat panel displays. Inaddition, our current invention could easily utilize the same process onany material that had a conductive seed layer and feature trenches andvias, such as decorative damascene inlays, damascene structures used inprinted wiring circuit boards, or in forming separate interconnectstructures that are later added to semiconductor devices or printedcircuit wiring boards. Metals that can be both electroplated andplanarized in an aqueous metal salt solution are compatible with thisprocess and include copper, silver, nickel, gold, and others, however,copper is the metal of choice for semiconductors.

The above description has been that of a preferred embodiment of thepresent invention. It will occur to those that practice the art thatmany modifications may be made without departing from the spirit andscope of the invention. For example, the system could be operated in aprogrammed voltage mode instead of a programmed current mode with thevoltage between the anode and cathode controlled by the system computerand programmable controller. In order to apprise the public of thevarious embodiments that may fall within the scope of the invention thefollowing claims are made.

We claim:
 1. A method of bipolar concurrent metal plating andplanarizing of a metallized surface of a semiconductor wafer, the methodincluding the steps of:(a) positioning a bipolar electrode assemblyproximate to said metallized surface, said bipolar electrode assemblyhaving an anode and cathode separated along an axis parallel to saidmetallized surface; (b) bathing a region between said anode and saidcathode and said metallized surface in an electroplating solution; (c)providing relative motion between said bipolar electrode assembly andsaid metallized surface, said relative motion being parallel to saidmetallized surface; and (d) applying a voltage across said anode andsaid cathode to plate metal from said electroplating solution onto afirst region of said metallized surface; said first region beingadjacent to said anode; and to concurrently electropolish said metalfrom a second region of said metallized surface; said second regionbeing adjacent to said cathode; through the action of flowing currentfrom said anode through said electroplating solution to said firstregion of said metallized surface, flowing said current through saidmetallized surface to said second region, and flowing said current tosaid cathode through said electroplating solution.
 2. The methodaccording to claim 1, wherein said relative motion is provided byholding said metallized surface stationary and moving said bipolarelectrode assembly.
 3. The method according to claim 1, wherein saidrelative motion is provided by holding said bipolar electrode assemblystationary and moving said metallized surface.
 4. The method accordingto claim 1, wherein said relative motion is provided by moving both saidmetallized surface and said bipolar electrode assembly.
 5. The methodaccording to claim 1, wherein said relative motion is selected from thegroup consisting of: linear motion, orbital motion, circular motion; anda combination of linear and circular motions.
 6. The method according toclaim 1, wherein the step of bathing a region between said anode andsaid cathode and said metallized surface in an electroplating solutionis performed via separate supply lines providing different electrolyticsolutions proximate the anode and cathode.
 7. The method according toclaim 1, including the step of positioning a brush between said bipolarelectrode assembly and said metallized surface with a surface of saidbrush adjacent to said metallized surface.
 8. The method according toclaim 1, wherein said voltage across said anode and said cathode iscontrolled in accordance with a direction of said relative motion. 9.The method according to claim 1, wherein said flowing current iscontrolled in accordance with a direction of said relative motion. 10.The method according to claim 1, including the step of supporting saidmetallized surface from a side opposite said metallized surface.
 11. Themethod according to claim 1, including the step of reusing saidelectroplating solution by recirculation means and conditioning means.12. The method according to claim 11, wherein said conditioning means isselected from the group consisting of: heating means, cooling means,chemical modification means, and means for filtration of saidelectroplating solution.
 13. The method according to claim 1, whereinsaid relative motion is chosen from the group consisting of: linearmotion, orbital motion, circular motion; and a combination of linear andcircular motions.
 14. The method according to claim 1, wherein saidrelative motion is chosen from the group consisting of: linear motion,orbital motion, circular motion; and a combination of linear andcircular motions.
 15. The method according to claim 1, wherein saidrelative motion is selected from the group consisting of: linear motion,orbital motion, circular motion; and a combination of linear andcircular motions.
 16. A method of bipolar concurrent metal plating andelectropolishing of a metallized surface, the method including the stepsof:(a) positioning a bipolar electrode assembly proximate to saidmetallized surface, said bipolar electrode assembly having an anode andcathode separated along an axis parallel to said metallized surface; (b)bathing a region between said anode and said cathode and said metallizedsurface in an electroplating solution; (c) providing relative motionbetween said bipolar electrode assembly and said metallized surface,said relative motion being parallel to said metallized surface; and (d)applying a voltage across said anode and said cathode to plate metalfrom said electroplating solution onto a first region of said metallizedsurface; said first region being adjacent to said anode; and toconcurrently electropolish said metal from a second region of saidmetallized surface; said second region being adjacent to said cathode;through the action of flowing current from said anode through saidelectroplating solution to said first region of said metallized surface,flowing said current through said metallized surface to said secondregion, and flowing said current to said cathode through saidelectroplating solution.
 17. The method according to claim 16, whereinsaid relative motion is provided by holding said metallized surfacestationary and moving said bipolar electrode assembly.
 18. The methodaccording to claim 16, wherein said relative motion is provided byholding said bipolar electrode assembly stationary and moving saidmetallized surface.
 19. The method according to claim 16, wherein saidrelative motion is provided by moving both said metallized surface andsaid bipolar electrode assembly.
 20. The method according to claim 16,wherein the step of bathing a region between said anode and said cathodeand said metallized surface in an electroplating solution is performedvia separate supply lines providing different electrolytic solutionsproximate the anode and cathode.
 21. The method according to claim 16,including the step of positioning a brush between said bipolar electrodeassembly and said metallized surface with a surface of said brushadjacent to said metallized surface.
 22. The method according to claim16, wherein said voltage across said anode and said cathode iscontrolled in accordance with a direction of said relative motion. 23.The method according to claim 16, wherein said flowing current iscontrolled in accordance with a direction of said relative motion. 24.The method according to claim 16, including the step of supporting saidmetallized surface from the side opposite said metallized surface. 25.The method according to claim 16, including the step of reusing saidelectroplating solution by recirculation means and conditioning means.26. The method according to claim 25, wherein said conditioning means isselected from the group consisting of: heating means, cooling means,chemical modification means, and means for filtration of saidelectroplating solution.